Heretofore, various forms of apparatus have been used in a reverse osmosis separation process. Osmosis is a diffusion proceeding in which the diffusion proceeds through a semipermeable membrane, typically separating two solutions of unequal concentration, the osmosis tending to equalize the concentration of the solutes in each solution. The semipermeable membrane possesses a finite permeability for one component of a solution, for example, water, while remaining totally impermeable to another component in the solution such as, for example, sodium chloride. During the process of osmosis, pure water diffuses from a first solution having a lower solute concentration through the membrane into a second solution having a higher solute concentration.
It is possible to restrain diffusion of the pure water through the membrane by maintaining the second solution, which possesses the higher solute concentration, at an elevated pressure with respect to the pressure conditions of the first solution. The particular pressure at which diffusion through a semipermeable membrane into the second solution is substantially retarded or halted is known as the osmotic pressure. However, if the pressure applied to the second solution is further increased relative to that applied to the first solution such that osmotic pressure of the second solution is exceeded, reverse osmosis occurs. The particular pressure which is required to bring about reverse osmosis is generally dependent upon the composition of the particular solutions disposed on opposite sides of the semipermeable membrane. A particularly applicable operation of reverse osmosis is in the gas of sea water. For example, if a sea water is disposed on one side of an appropriate semipermeable membrane and a relatively pure water solution, or a gaseous atmosphere is present on the other side, reverse osmosis begins to occur when the sea water is subjected to a pressure of approximately 350 psi absolute. As a result of this reverse osmosis, pure water diffuses through the membrane from the sea water.
Certain types of apparatus which may be utilized for reverse osmosis applications such as desalinization of sea water, are known from such patents as U.S. Pat. Nos. 3,367,504, 3,386,583 and 3,417,870, among others. However, these patents utilize, as a backing material for semipermeable membranes which form a product water passageway, such materials as cotton, wool, graphite, cloth, silicon carbide grit or salt particles held together with a suitable binder, glass felt, or fibrous plastic material such as nylon, polyester, rayon, rayon viscose, acrylic fibers, etc.
As will hereinafter be shown in greater detail, a reverse osmosis apparatus has been prepared which will permit the use of such an element in a high temperature operation at relatively high applied pressures. The operability of this element is due to the use of certain composites which provide a novel arrangement of materials to form the product water-carrying channels.